The inventors of the present application have found at least the following technical problems in the related art in the process of implementing the technical solution of the embodiment of the present application.
For a communication receiving system, the noise factor and gain of a first stage circuit behind an antenna determines the receiving sensitivity of the entire system, and the use of a Low Noise Amplifier (LNA) herein not only amplifies weak received signals, but also its low noise factor also determines the noise factor of the entire system and improves receiving performance.
To make the LNA operate under the best noise performance, impedance matching is required to be performed on its input end, so that after impedance matching, the input impedance achieves an optimum value for noise characteristics of transistors used in the LNA; if matching is not performed for the best noise factor, the noise performance of the LNA cannot be fully developed, thereby reducing the receiving sensitivity, and thus reducing the receiving performance of the entire receiving system.
With the development of the modern communication system, it is required that the communication reception system often operates in multiple frequency bands, such as CDMA, WCDMA, GSM, GPS, WLAN, etc. If it is required to ensure that multiple receivers can operate in the best condition in multiple frequency bands, it is undoubted that the complexity of the circuit design will be increased. However, the development of the modern wireless communication system also presents a trend of miniaturization and portable-type, and the space for circuit design has been compressed. The circuit has increasingly improved requirement on circuit integration.
However, in the prior art, various mobile communication receiving systems often employ multiple LNAs with multiple operating characteristics in different frequency bands to enable an receiver to have good receiving performance on different frequency bands. This requires that a corresponding input and output matching circuit is designed for an LNA operating in a respective frequency band, that is to way, an LNA operating in multiple different operating frequency bands needs to be provided with multiple peripheral devices such as input and output matching circuits, otherwise, matching of different operating frequency bands cannot be achieved, resulting in the following problem.
The use of T-type or π-type matching network will increase the number of such peripheral devices. Even if devices with 0201 package are used, it will greatly increase the area of the external matching circuit; and an increase in the complexity of the matching circuit will directly affect the difficulty of PCB layout, thus improve the possibility that problems such as interference, impedance mismatch and so on are introduced into the circuit.
In short, the prior art cannot solve the contradictions between the performance of the receiving system and the hardware complexity. For this problem, the related art has not proposed effective solutions.